In recent years, electronic apparatuses are desired to achieve power saving as international environmental cooperation has been considered. For example, in the final stage of a transmitting unit of a base station in a mobile phone system, an amplifying device is provided to amplify a transmission signal, and power consumption reduction of the amplifying device is desired.
Envelope tracking is an example of a method for improving power efficiency of the amplifying device. The envelope tracking is a technique for supplying a power source voltage according to an amplitude of the signal to be amplified by the amplifier of the amplifying device so that power loss is reduced.
For example, the envelope tracking supplies simply the power of a fixed voltage by a high efficient power source if the envelope of the amplified signal is equal to or smaller than a prescribed threshold value (a fixed voltage power mode). If the envelope of the amplified signal exceeds the prescribed threshold value, the envelope tracking supplies the power of a variable voltage according to the amplified signal to the amplifier from a low efficient power source. In this manner, the envelope tracking improves the power efficiency by switching the power source based on the size of the envelope of the signal to be amplified.